<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<form action="area" method="post">
		请输入一个圆的半径：<input type="text" name="radius">
		<input type="submit" value="计算面积">
	</form>
</body>
</html>